Aircraft glide slope coupler system

ABSTRACT

A glide slope coupler adaptable to both Autopilot and Flight Director modes for guiding an aircraft to a landing along a radio defined glide slope beam. An integrator common to both modes effectively memorizes the aircraft descent rate and provides a signal representative thereof for summation with glide slope beam displacement and altitude rate signals in respective amplifiers coupled to drive the pitch actuators and Flight Director Indicator bar. A synchronizing mode is included for coupling the pitch actuator driver amplifier output to the integrator input to obtain a desired descent rate signal while flying in a cruise mode prior to intercepting the glide slope beam. Upon intercepting the beam either the Autopilot or Flight Director mode is activated as chosen by the pilot and the selected system then operates to reduce the beam displacement signal to zero with flight path damping being provided by the altitude rate signal. During the descent the beam displacement signal is modified as a function of altitude to compensate for the convergence of the glide slope beam. At a predetermined flare altitude the beam displacement signal is rendered ineffective and thereafter the integrator output signal is modified as a function of altitude to control the flare in accordance with the memorized value of the descent rate at the commencement of the flare maneuver.

United States Devlin et al.

atent [54] AIRCRAFT GLIDE SLOPE COUPLER Primary ExaminerMalcolm A.Morrison SYSTEM Assistant Examiner-Jerry Smith An --S. C. Ye t [72]Inventors: Bernard T. Devlin; William F. Poland, omey a on both ofPhoenix, Ariz. 57] ABSTRACT [73] Assignee: Sperry Rand Corporation Aglide slope coupler adaptable to both Autopilot and Flight [22] Filed:May 14, 1970 Director modes for guiding an aircraft to a landing along aradio defined glide slope beam. An integrator common to both [21 1 Appl'37073 modes effectively memorizes the aircraft descent rate and providesa signal representative thereof for summation with glide [52] US. CL....235/l50.22, 244/77 A, 343/108 R slope beam displacement and altituderate signals in respec- [51] Int. Cl. ..G06g 7/78, GOls l/l8 tiveamplifiers coupled to drive the pitch actuators and Flight [58] Field ofSearch ..35/ 10.2; 235/ 150.22, 183; Director Indicator bar. Asynchronizing mode is included for 340/27 AT, 27 NA; 343/107, 108 R, 108M, 112 C, coupling the pitch actuator driver amplifier output to the in-112 77 77 B, 77 C tegrator input to obtain a desired descent rate signalwhile flying in a cruise mode prior to intercepting the glide slopebeam. References Cited Upon intercepting the beam either the Autopilotor Flight Director mode is activated as chosen by the pilot and theUNITED STATES PATENTS selected system then operates to reduce the beamdisplace- 3,295,796 1/1967 Gaylor ..244/77 ment signal to zero withflight path damping being provided by 3,280,310 l0/1966 Montooth .235/150.22 the altitude rate signal. During the descent the beam displace3,333,795 8/ l 967 Hattendorf et al. .....244/77 ment signal is modifiedas a function of altitude to compensate 3,059,881 10/ 1962 Letson..244/77 for the convergence of the glide slope beam. At a predeter-3,266,753 8/l966 Gaylor ..343/108 X mined flare altitude the beamdisplacement signal is rendered 3,355,733 1 H1 67 Mitchell et 51]..235/1 50.22 X ineffective and thereafter the integrator output signal is3,361,391 1/1968 Medlmskl 107 X modified as a function of altitude tocontrol the flare in ac- 3I447I765 6/ 1969 DQ111861 et 31H -244/ 77cordance with the memorized value of the descent rate at the Watson etal- X commencement ofthe flare maneuver 3,523,664 8/1970 Doniger et al...343/108 X 14 Claims, 2 Drawing Figures R A D I O A L T I M ETE R i h Rl l '5 I Q I 65' 1500 14 L 36 S CRUISE ELEvAToR A F ARE A AcT- BEAMMLULT. UATOR T e522 24 1 3 29 R E c E I v E R 28 l l 254 T 0 1m A ASWITCHES 1" 4o sEcr I i 3 0 m v 32 BEAM i {W 251., I-VDT S E N SO R 51 1"v"\X/\I 17 BARO COMPLI- R A T E N o ALTITUDE MENTARY wt AME 'VW\, RATE(h) FILTER B 36 1260 l/ 47 mia'ciii/ s 41 44 m i 8 NORMAL VERSINE LAGAQPEL COMP FILTER 131;

(h 1' M A AUTOPILOT I45 39 151, cRuIsE P I TO H :LTTCEH BANDPASS M MM615 5-3 I FLIGHT (a) 42 FILTER 1 11 DlgEgTOR AIRCRAFT GLIDE SLOPECOUPLER SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention Thepresent invention relates to apparatus for guiding an aircraft to alanding along a radio defined glide slope beam and more particularly toglide slope coupler apparatus adaptable for operation in both Autopilotand Flight Director modes for guiding a craft during the course of thebeam capture, descent and flare phases of the landing procedure.

2. Description of the Prior Art Prior art devices relating to glideslope coupler systems are exemplified by U.S. Pat. No. 3,058,699, issuedOct. 16, 1962, in the name of S. S. Osder; U.S. Pat. No. 3,059,881,issued Oct. 23, 1962, in the name of R. A. Letson; U.S. Pat. No.3,052,427, issued Sept. 4, 1962, in the name of M. J. Match et al. andU.S. Pat. No. 3,115,319, issued Dec. 24, 1963, in the name of M. B.Glaser et al.; all of which are assigned to the assignee of the presentinvention. The Osder and Letson patents relate to apparatus forcapturing the glide slope beam while the Match and Glaser patents areconcerned with apparatus for flaring out of the beam to effect a desiredtouchdown.

In both Osder and Letson the primary control for capturing or flaringinto the beam is provided by an altitude rate error signal derived froma comparison of signals representative of a desired rate of descent andthe actual measured rate of descent. More specifically, Osder effectsthe beam capture by determining when the craft has intercepted thecenter line of the glide slope beam and then switching in the glideslope receiver so that pitch control is provided by a signal indicativeof craft displacement from the beam, the integral of the displacementsignal and the altitude rate error signal plus attitude and dampingterms. As mentioned above, the altitude rate error signal provides thepredominant pitch control during the capture phase for the purpose ofrapidly reducing the overshoot which occurs as a consequence of delayingthe start of the pitch maneuver until the center of the glide slope beamhas been intercepted. After a brief interval, however, on the order ofseconds, the altitude rate error signal is switched out of the pitchcontrol loop and the descent proceeds under the primary control of thebeam displacement and integral of beam displacement signals. This systemhas a comparatively large inherent overshoot attendant to its mode ofoperation.

Letson employs the same pitch control signals as Osder but reduces theovershoot by switching in the altitude rate error signal for apredetermined time to control the pitch loop prior to intercepting thecenter of the beam and thereafter utilizing the beam displacement andintegral signals for controlling the descent of the craft along theglide slope beam. It will be apparent to those skilled in the art thateven for a standard altitude hold capture, that is a capture maneuverinitiated at a time when the craft is in level flight, a beam standoffis likely to exist at the end of the altitude rate error control period.

In the present invention the above mentioned limitations of the priorart systems are overcome by continuously employing the beam displacementsignal in conjunction with memorized rate of descent and actual rate ofdescent signals from the commencement of the capture maneuver. Moreover,once the Autopilot or Flight Director glide slope coupler of the presentinvention is actuated the necessity for further switching of varioussignals is obviated thereby enhancing the reliability of the system.

Regarding the prior art flare out systems, Match et al., for example,employs the glide slope beam displacement signal to control the FlightDirector Indicator bar during the descent until a predeterminedtransition altitude is reached at which time it is rendered ineffective.During the descent down to the transition altitude the actual altituderate is memorized and after the transition point the memorized signal iscompared with a signal indicative of the actual measured rate of descentto provide a control signal for the Flight Director bar. This techniqueis used because of the likelihood of the glide slope receiver signalcontaining spurious information at altitudes below the transitionaltitude. At a subsequent lower altitude the flare maneuver is initiatedby introducing a constant term into the rate of descent control signalso as to cause the craft to pitch up slightly and thus flare out forlanding. Operation in this manner, however, can produce undesirably hardlandings, or alternatively can preclude a touchdown. For instance, ifthe nominal desired touchdown descent rate is 2 feet per secondcorresponding to a descent rate prior to flare of say 1 1 feet persecond, then the flare command, that is the constant added to thedescent rate signals, must produce a 9 foot per second change in thedescent rate. If for some reason, perhaps a strong tailwind, the actualdescent rate is greater than the nominal value of l 1 feet per secondsuch that it has a value for example of 14 feet per second, the 9 feetper second reduction will provide a 5 feet per second touchdown descentrate, which is unsuitable. On the other hand, if the actual descent rateis only 8 feet per second at the inception of flare, the 9 feet persecond reduction will result in an ascent rate of 1 foot per second andthus prevent the craft from landing.

In the present invention a closed-loop flare control is used as opposedto the open-loop flare controls of the prior art to prevent theoccurrence of the above-described conditions. Further as in the case ofthe prior art beam capture systems, it is seen that considerable signalswitching is required in the Match et al. apparatus and this is truealso for the aforementioned Glaser apparatus. The present invention, onthe other hand, accomplishes the flare maneuver without signal switchingthus provides a completely switchless device during the capture, descentand flare phases of operation. As will be explained subsequently, theonly switching attendant to the apparatus of the present inventionoccurs in a synchronizing mode upon initiation of the capture phase forplacing the system in Autopilot or Flare Director control. Moreover,because of the integrator technique employed in the present inventionthe necessity for a transition altitude reference is obviated. This willbe understood more fully after reading the subsequent Description of thePreferred Embodiment.

SUMMARY OF THE INVENTION A preferred glide slope coupler constructed inaccordance with the principles of the present invention incorporates a1titude rate damping in apparatus adaptable for use in both Autopilot andFlight Director modes to provide a high performance system with minimumcomplexity, maximum commonality of parts, and compatibility of flightcontrol laws. The coupler includes a synchronizing mode which isactuated during cruise flight prior to intercepting the glide slopebeam. In the synchronizing mode the output of the pitch actuator driveramplifier is coupled back to the input of an integrator which providesan output signal for summing with the glide slope beam displacementsignal and an altitude rate signal in the driver amplifier. Thus, for alevel flight condition, in other words a standard altitude hold captureor zero altitude rate, the beam displacement signal is balanced againstthe integrator output in a manner to provide a signal thereatrepresentative of a nominal desired descent rate. The integrator is alsoused in both the Autopilot and Flight Director modes to provide acontrollable desired descent rate signal determined in accordance withthe actual descent rate. In the Autopilot mode this is accomplished byconnecting the integrator to receive the beam displacement signal fromthe glide slope receiver while in the Flight Director mode it isaccomplished by switching the integrator output into its input alongwith the altitude rate signal.

More specifically, in Flight Director operation an amplifier connectedto drive the Flight Director Indicator bar has coupled to its input asignal derived froni the output of the integrator together with the beamdisplacement and altitude rate signals. Now, as a result of the previoussynchronizing operation, the integrator output signal corresponds to theglide slope descent rate. When the craft intercepts a predeterminedradial of the beam, it is switched into the Flight Director mode, aspreviously selected by the pilot, resulting in the aforementioned signalinput to the integrator, namely altitude rate and integrator output,whereupon a signal is provided at the integrator output to wash out thealtitude rate signal coupled to the input of the Flight Directoramplifier. Hence, the glide slope beam displacement signal is thepredominate control for the indicator bar with the altitude rate signalproviding path damping. The system therefore operates during the descentto reduce the beam displacement to zero with the integrator outputsignal washing out the steady state descent rate signal.

In the Autopilot mode the actuator driver amplifier is coupled toreceive a signal derived from the integrator along with the glide slopebeam displacement and altitude rate signals. As in the case of theFlight Director, the previous synchronizing operation has driven theintegrator output signal to a level corresponding to the glide slopedescent rate and then as the craft intercepts the beam the coupler isswitched into the Autopilot mode in accordance with the pilotsselection. In the Autopilot mode the glide slope beam displacementsignal is switched onto the integrator input and the system operates tointegrate the beam displacement to zero so that the system is satisfiedwhen the beam displacement is zero and the beam integrator cancels thedescent rate. Thus for both Autopilot and Flight Director operation theintegrator effectively memorizes the descent rate.

Moreover, in both the Autopilot and Flight Director modes the glideslope displacement signal is continuously modified as a function ofaltitude, starting at a prescribed altitude, to compensate for theconvergence of the glide slope beam as the craft approaches the ground.Likewise, in both modes a flare command is initiated at a predeterminedaltitude whereupon the glide slope displacement signal is renderedinefiective and the integrator output is continuously modifiedthereafter as a function of altitude to achieve a flare which isdetermined by the instantaneous descent rate at the beginning of theflare maneuver to assure touchdown within tolerable limits of a nominaltouchdown descent rate.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing thegeneral arrangement of components in a preferred embodiment of theinvention. FIG. 2 is a diagram of a typical glide path depicting thepoints at which the capture and flare maneuvers are initiated.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the figures, theglide slope coupler apparatus of the present invention comprises anautopilot actuator driver amplifier l and a flight director indicatordriver amplifier 11 connected through respective resistors 12a, b and cand 13a, b and c to points A, B and C which in turn are connectedrespectively to the outputs of flare multiplier 14, beam multiplier 16and amplifier 17 to receive appropriate operational control signals aswill be described in the ensuing paragraphs. During normal cruise flightswitches S-2 and 8-3 are in the CRUISE position so that the coupler isinoperative.

Consider the operation of the coupler prior to intercepting the glideslope beam, momentarily disregarding the function of the radio altimeter18 and programmable limiters 19 and 21. At this time the coupleroperates in a synchronizing mode as indicated by switch S-l beingengaged with the SYNC contact. In this mode the output of the actuatordriver amplifier is connected through resistor 22 and switch 8-1 to theinput of integrator 23 which has its output connected by lead 24 to theinput of the flare multiplier. At the synchronizing altitude, typicallyabout 1,500 feet or more, programmable limiter 21 multiplies theintegrator output by unity so that the integrator is effectively coupleddirectly to point A. Likewise, at the synchronizing altitudeprogrammable limiter 19 multiplies the beam displacement signal providedat the output of glide slope receiver 24 by a factor of unity so thatthe receiver output is effectively coupled directly to point B. Inaddition, as indicated in the drawing, amplifier 17 has connected to itsinput through resistors 26a, b and c respective altitude rate, normalacceleration and pitch rate signals. For a standard altitude hold glideslope capture, that is with the aircraft cruising in level flight duringthe synchronizing mode, all of these signals in addition to the feedbacksignal from the linear variable differential transformer 25 will besubstantially equal to zero thus providing a signal level of zero atpoint C. Hence, with the aircraft in level flight the two input signalsto actuator driver amplifier 10 are the integrator/flare multiplieroutput provided at point A and the glide slope beam displacement signalprovided "at point B. Actually the glide slope beam is considerablywider, about :200 millivolts, than the :30 millivolt width depicted inFIG. 2. During the time the craft is flying from the +200 millivolt beamfringe to the +30 millivolt radial the coupler is synchronizing with theintegrator output continuously changing to nullify the varying beamdisplacement signal, the coupler system gains being adjusted such thatfor a given craft velocity the +30-millivolt beam displacement signalbalanced against the integrator/flare multiplier output signalcorresponds to a desired descent rate along the glide slope beam, say l1 feet per second. At the +30 millivolt radial the beam sensor 27provides an output signal to actuate switches S-2 and 8-3 to the GLIDESLOPE position thereby enabling amplifier 10 to control actuator 28which drives elevator 29 and likewise enabling amplifier 11 to drive theFlight Director Indicator bar. At the same instant switch 8-1 isactuated to either the AUTOPILOT or FLIGHT DIRECTOR position inaccordance with a prior selection made by the pilot. It should beunderstood that the above reference to a standard altitude capture isnot to be construed as signifying that the coupler can operate onlyunder such conditions. Those skilled in the art will recognize that thesystem will operate to achieve the desired result even under differentdynamic conditions prevailing during the synchronizing mode. Thestandard al-. titude hold capture is alluded to simply for ease ofdescription and understanding.

First consider the Flight Director mode. On actuation of Switch 8-1 tothe FLIGHT DIRECTOR position the integrator output signal and thealtitude rate signal provided at the out-- put of complimentary filter31 are coupled through summing network 32, comprising resistors 32a andb, into the input of the integrator. The complimentary filter provides atransfer function of 1/1 ls+l relative to the altitude rate signal (hwhich it derives through resistor 36 from a barometric altitude ratesensor 37 of the type described in Osder and Letson (Item 41). Furtherit provides a transfer function of 1 l/ l ls+l relative to the normalacceleration signal h, derived from normal accelerometer 38 throughversine computer 39 and resistor \41. The output signal of thecomplimentary filter resulting from the sum of these transfer functionsis II 11% E 111s+1 11s-l-1 118+1 1 Ii Ii 1 s (118+1) or simplyh(altitude rate). By summing the altitude rate and normal accelerationsignals in this manner the instantaneous altitude rate signal producedat the output of the complimentary filter is a function of barometricrate at low frequencies and inertial rate at high frequencies. Asindicated in the drawing, the versine computer is controlled inaccordance with the craft roll angle (4)) to compensate for the reducedeffect of the earth's gravity on the normal accelerometer as theaircraft rolls from a level condition. This feature is not required, ofcourse, when the normal acceleration signal is obtained from a stableplatform. Short period mode damping during glide slope and flarecontrol, and tight control to the beam for wind gusts or wind sheer, areprovided by filtered pitch rate (0) and normal acceleration signalsderived respectively from pitch rate sensor 42 through bandpass filter43 and from the normal accelerometer/versine computer output throughfilter 44.

Initially as the craft moves from point of interception with the 30millivolt beam radial toward the beam center line 34, the beamdisplacement signal decreases thereby lowering the voltage at point B.This reduction of a fly-up command constitutes a fly-down commandcausing the aircraft to pitch down for the purpose of getting onto thecenter line of the glide slope beam. At this time the altitude ratesignal becomes effective with the ultimate result that the integratorproduces a signal at point A which washes out the altitude rate signalat point C. In other words, as the craft pitches down and approaches thebeam center line the altitude rate signal increases while simultaneouslythe beam displacement signal decreases until finally when the craft ison the glide slope center line the beam displacement signal is zero andthe altitude rate signal at point C is balanced against theintegrator/flare multiplier output signal at point A. Thereafter,assuming a fairly steady descent rate, the Flight Director bar iscontrolled by the beam displacement signal with the washed out altituderate signal providing flight path damping. The capture maneuver is thusperformed under the continuous control of the beam displacement signalaided by the actual and desired altitude rate signals with a resultingasymptotic capture of the beam center line as indicated by the dashedline flight path in FIG. 2. Operation in the foregoing manner isobtained by selecting resistor 32b to provide long time constantintegrator feedback, on the order of 40 seconds. This effectivelyconverts the integrator to a lag network with respect to the altituderate signal applied thereto through resistor 32a. Hence, the integratoroutput signal is able to change from the nominal descent rate valueacquired during the standard altitude hold capture but any change whichdoes occur is small because of the operation of the integrator-lagnetwork. In the meantime, any change of the actual descent rateimmediately produces a signal at point C to provide the flight pathdamping. The net result of this action is that the integrator outputsignal varies to wash out the actual measured descent rate, whatever itmay be, so that the beam displacement signal can effectively control theFlight Director Indicator bar during the glide slope descent and therebyenable a beam standoff to be avoided.

When the capture maneuver commences, preferably at the prescribed 1,500foot altitude, limiter 19 operates to modify the beam displacementsignal as a function of altitude in response to a signal derived fromradio altimeter 18 so as to compensate for the convergence of the glideslope beam, that is the signal strength per foot of displacement fromthe center line of the beam, as the craft approaches the landing strip.This can be accomplished simply by varying the limiter voltage output (Vfrom unity down to zero in accordance with altitude as indicated in thedrawing. Any conventional circuit capable of performing the indicatedfunction can be used. In this way the beam displacement signal will bemultiplied by successively smaller numbers as the craft altitudedecreases. Finally, at the flare point, 65-feet altitude for example,the beam multiplier output reduces to zero as a consequence of the beamdisplacement signal being multiplied by zero voltage output from limiter19. At the same instant the voltage output oflimiter 21 is reduced fromunity down to 0.2 as a function of altitude, in response to the radioaltimeter signal, causing the signal at point A to decrease. Thisconstitutes a fly-up command causing the craft to flare out prior totouchdown. Thus, the desired glide slope descent rate of l 1 feet persecond will produce a touchdown descent rate of 2.2 feet per second. Ifthe descent rate increases to l4 feet per second as discussed withreference to the prior art systems, the touchdown descent rate willincrease to only 2.8 feet per second; and, likewise, if the descent rateat the beginning of the flare is 8 feet per second, touchdown will stillbe assured with a touchdown descent rate of 1.6 feet per second. Theflare control of the present invention thus provides suitable touchdowndescent rates independent of variations of the actual craft descent ratewithin given limits from the desired descent rate and further assures arestricted longitudinal touchdown point distribution.

Operation in the Autopilot mode is essentially the same as describedwith reference to the Flight Director mode except for certaindifferences which will now be discussed. In the Autopilot mode, uponintercepting the 30 millivolt radial of the glide slope beam subsequentto synchronizing, the beam sensor 27 actuates switch S-l to theAUTOPILOT position connecting the output of beam multiplier 16 throughresistor 46 to the integrator input. Then as the craft flys toward thecenter of the beam, reducing the beam displacement signal, the resultantfly-down command (beam displacement signal less than the signal at pointA) causes the craft to pitch down whereupon an altitude rate signal isprovided at point C. The beam displacement integrator gain is madesufficiently low so that the integrator output signal remainsessentially at its initial value during the entire capture phase.Accordingly, the coupler operates to reduce the beam displacement signalto zero with the altitude rate signal at point C being cancelled by theintegrator/flare multiplier output signal at point A. The low gain ofthe integrator enables the altitude rate signal to provide flight pathdamping for changes which may occur in the descent rate. In all otherrespects, including the operation of the limiters and the damping terms,the operation of the Glide Slope Coupler is the same in both Autopilotand Flight Director modes.

It is thus seen that the integrator which is considered an essentialcomponent of the coupler for Autopilot operation is also employed forFlight Director operation. In both instances the integrator effectivelymemorizes a signal representative of the desired descent rate andthereby enables similar operation of the coupler in both modes, namelybeam displacement control aided by altitude rate flight path damping inconjunction with short-term normal acceleration and pitch rate damping.In addition, the integrator is utilized during the preliminarysynchronizing mode to achieve continuous beam displacement control fromthe inception of the capture phase.

In a case where it is desired to use the Flight Director Indicator as amonitor of Autopilot performance, the actuator feedback signal derivedfrom the linear variable differential transformer is coupled throughswitch S-4, lag network 47 and resistor 48 into Flight Directoramplifier l 1. This removes the Autopilot trim signal from the FlightDirector Indicator.

While the invention has been described in its preferred embodiment, itis to be understood that the words which have been used are words ofdescription rather than limitation and that changes may be made withinthe purview of the appended claims without departing from the true scopeand spirit of the invention in its broader aspects.

We claim:

1. Apparatus for guiding a craft to a landing along a radio definedglide slope beam, comprising an integrator for storing a signalrepresentative of a desired descent rate along the glide slope beam,

means for providing a signal representative of the craft displacementfrom the center line of the glide slope beam, means for providing asignal representative of the actual descent rate of the craft,

means for algebraically summing the stored signal of said integratorwith the actual descent rate and beam displacement signals, and

means for selectively coupling the output of said summing means to theinput of said integrator prior to the craft intercepting a predeterminedradial of the glide slope beam for controlling the output signal levelof the integrator in accordance with the instantaneous amplitude of thebeam displacement and actual descent rate signals whereby upon the craftintercepting said predetermined radial at a given velocity in a levelflight condition a desired descent rate signal is produced at the outputof said integrator to cause pitch down of the craft for capturing theglide slope beam.

2. The apparatus of claim 1 wherein the selective coupling means isfurther operative upon disconnecting the output of said summing meansfrom the input of said integrator for applying either the displacementsignal or the combination of the actual descent rate signal and theintegrator output signal to the integrator input for varying the desireddescent rate signal so as to wash out the steady state actual descentrate signal whereby the output signal of said summing means isindicative of the craft displacement from the center line of the glideslope beam.

3. The apparatus of claim 2 including means for reducing the magnitudeof the beam displacement signal in proportion to decreasing craftaltitude below a predetermined altitude to compensate for convergence ofthe glide slope beam approaching ground level.

4. The apparatus of claim 3 further including means for deactivating thebeam displacement signal at a second lower predetermined altitude andsimultaneously continuously modifying the desired descent rate signal asa function of altitude from said second predetermined altitude totouchdown such that the touchdown descent rate is a prescribed fractionof the instantaneous descent rate prevailing at a predeterminedaltitude.

5. The apparatus of claim 1 wherein the selective coupling means isfurther operative upon disconnecting the output of said summing meansfrom the input of said integrator for connecting the integrator outputto its input and simultaneously applying the actual descent rate signalthereto so that the integrator output signal is driven to a level equalto that of the steady state actual descent rate signal whereby thedisplacement signal provides the predominant control for guiding thecraft down the glide slope beam.

6. The apparatus of claim 5 wherein the output of said integrator isconnected to its input through an impedance of sufticient value toconvert the integrator to a long time constant lag network.

7. The apparatus of claim 5 further including means for deactivating thebeam displacement signal at a second lower predetermined altitude andsimultaneously continuously modifying the desired descent rate signal asa function of altitude from said second predetermined altitude totouchdown such that the touchdown descent rate is a prescribed fractionof the instantaneous descent rate prevailing at the predeterminedaltitude.

8. The apparatus of claim 1 wherein the selective coupling means isoperative upon disconnecting the output of said summing means from theinput of said integrator for connecting the displacement signal means tothe integrator input so that the integrator output is driven to a levelequal to that of the steady state actual descent rate signal whereby thedisplacement signal provides the predominant control for guiding thecraft along the center line of the glide slope beam.

9. The apparatus of claim 8 further including means for deactivating thebeam displacement signal at a second lower predetermined altitude andsimultaneously continuously modifying the desired descent rate signal asa function of altitude from said second predetermined altitude totouchdown such that the touchdown descent rate is a prescribed fractionof the instantaneous descent rate prevailing at the predeterminedaltitude.

10. An integrated Autopilot/Flight Director glide slope coupler systemfor guiding a craft to a landing along a radio defined glide slope beam,comprising means for providing a signal representative of the craftdisplacement from the center line ofthe beam,

switching means enabling said system to be set initially in asynchronizing mode and thereafter in either an Autopilot or FlightDirector mode,

means for providing a signal representative of the actual descent rateof the craft, an integrator for storing a signal representative of adesired descent rate, means for algebraically summing the integratoroutput signal with the displacement and actual altitude rate signals,and said switching means being operative in a first conditioncorresponding to the synchronizing mode, prior to the craft interceptinga predetermined radial of the glide slope beam, to connect the output ofsaid summing means to the input of said integrator for controlling theoutput signal level thereof in accordance with the instantaneousamplitude of the beam displacement and actual descent rate signalswhereby upon the craft intercepting said predetermined radial in a levelflight condition at a prescribed velocity the signal at the output ofsaid integrator is representative of a desired descent rate to cause acraft pitch down to fly along the center line of the glide slope beam.

11. The apparatus of claim 10 further including additional algebraicsumming means connected to receive the actual descent rate, displacementand desired descent rate signals to produce a resultant flight directorindicator control signal, and

means for summing the actual descent rate and desired descent ratesignals and applying them to the input of said integrator during asecond condition of said switching means corresponding to the flightdirector mode so that the steady state effect of the actual rate ofdescent signal is effectively nullified in said additional summingmeans.

12. The apparatus of claim 11 further including means for continuouslymodifying the displacement signal in accordance with the instantaneousaltitude of the craft from a first predetermined altitude down to asecond predetermined altitude to compensate for convergence of the glideslope beam, and

means for continuously modifying the output signal of said integrator inaccordance with the instantaneous craft altitude from the secondpredetermined altitude to touchdown such that the touchdown descent rateis a prescribed fraction of the instantaneous descent rate prevailing atthe second predetermined altitude.

13. The apparatus of claim 10 wherein the switching means is operativeupon completion of the synchronizing mode to disconnect the output ofthe algebraic summing means from the integrator input and to connectthereto the output of said beam displacement means in a third conditionof said switching means corresponding to the autopilot mode such thatthe effect of the steady state actual rate of descent signal iseffectively nullified in said algebraic summing means.

14. The apparatus of claim 13 including means for continuously modifyingthe displacement signal in accordance with the instantaneous altitude ofthe craft from a first predetermined altitude down to a secondpredetermined altitude to compensate for convergence of the glide slopebeam, and

means for continuously modifying the output signal of said integrator inaccordance with the instantaneous craft altitude from the secondpredetermined altitude to touchdown such that the touchdown descent rateis a prescribed fraction of the instantaneous descent rate prevailing atthe second predetermined altitude.

Disclaimer 3,652,835.Be1"nard T. Devlin and William F. Poland, Phoenix,Ariz. AIR- CRAFT GLIDE SLOPE COUPLER SYSTEM. Patent dated Mar. 28, 1972.Disclaimer filed Sept. 27, 1974, by the assignee, Spew'g RandCorpomlz'on. Hereby enters this disclaimer to claims 1, 8, 10, 13 and 14of said patent. [Ofiicz'al Gazette J anuawy 14, 1.975.]

1. Apparatus for guiding a craft to a landing along a radio definedglide slope beam, comprising an integrator for storing a signalrepresentative of a desired descent rate along the glide slope beam,means for providing a signal representative of the craft displacementfrom the center line of the glide slope beam, means for providing asignal representative of the actual descent rate of the craft, means foralgebraically summing the stored signal of said integrator with theactual descent rate and beam displacement signals, and means forselectively coupling the output of said summing means to the input ofsaid integrator prior to the craft intercepting a predetermined radialof the glide slope beam for controlling the output signal level of theintegrator in accordance with the instantaneous amplitude of the beamdisplacement and actual descent rate signals whereby upon the craftintercepting said predetermined radial at a given velocity in a levelflight condition a desired descent rate signal is produced at the outputof said integrator to cauSe pitch down of the craft for capturing theglide slope beam.
 2. The apparatus of claim 1 wherein the selectivecoupling means is further operative upon disconnecting the output ofsaid summing means from the input of said integrator for applying eitherthe displacement signal or the combination of the actual descent ratesignal and the integrator output signal to the integrator input forvarying the desired descent rate signal so as to wash out the steadystate actual descent rate signal whereby the output signal of saidsumming means is indicative of the craft displacement from the centerline of the glide slope beam.
 3. The apparatus of claim 2 includingmeans for reducing the magnitude of the beam displacement signal inproportion to decreasing craft altitude below a predetermined altitudeto compensate for convergence of the glide slope beam approaching groundlevel.
 4. The apparatus of claim 3 further including means fordeactivating the beam displacement signal at a second lowerpredetermined altitude and simultaneously continuously modifying thedesired descent rate signal as a function of altitude from said secondpredetermined altitude to touchdown such that the touchdown descent rateis a prescribed fraction of the instantaneous descent rate prevailing ata predetermined altitude.
 5. The apparatus of claim 1 wherein theselective coupling means is further operative upon disconnecting theoutput of said summing means from the input of said integrator forconnecting the integrator output to its input and simultaneouslyapplying the actual descent rate signal thereto so that the integratoroutput signal is driven to a level equal to that of the steady stateactual descent rate signal whereby the displacement signal provides thepredominant control for guiding the craft down the glide slope beam. 6.The apparatus of claim 5 wherein the output of said integrator isconnected to its input through an impedance of sufficient value toconvert the integrator to a long time constant lag network.
 7. Theapparatus of claim 5 further including means for deactivating the beamdisplacement signal at a second lower predetermined altitude andsimultaneously continuously modifying the desired descent rate signal asa function of altitude from said second predetermined altitude totouchdown such that the touchdown descent rate is a prescribed fractionof the instantaneous descent rate prevailing at the predeterminedaltitude.
 8. The apparatus of claim 1 wherein the selective couplingmeans is operative upon disconnecting the output of said summing meansfrom the input of said integrator for connecting the displacement signalmeans to the integrator input so that the integrator output is driven toa level equal to that of the steady state actual descent rate signalwhereby the displacement signal provides the predominant control forguiding the craft along the center line of the glide slope beam.
 9. Theapparatus of claim 8 further including means for deactivating the beamdisplacement signal at a second lower predetermined altitude andsimultaneously continuously modifying the desired descent rate signal asa function of altitude from said second predetermined altitude totouchdown such that the touchdown descent rate is a prescribed fractionof the instantaneous descent rate prevailing at the predeterminedaltitude.
 10. An integrated Autopilot/Flight Director glide slopecoupler system for guiding a craft to a landing along a radio definedglide slope beam, comprising means for providing a signal representativeof the craft displacement from the center line of the beam, switchingmeans enabling said system to be set initially in a synchronizing modeand thereafter in either an Autopilot or Flight Director mode, means forproviding a signal representative of the actual descent rate of thecraft, an integrator for storing a signal representative of a desireddescent rate, means for algebraically summing the integrAtor outputsignal with the displacement and actual altitude rate signals, and saidswitching means being operative in a first condition corresponding tothe synchronizing mode, prior to the craft intercepting a predeterminedradial of the glide slope beam, to connect the output of said summingmeans to the input of said integrator for controlling the output signallevel thereof in accordance with the instantaneous amplitude of the beamdisplacement and actual descent rate signals whereby upon the craftintercepting said predetermined radial in a level flight condition at aprescribed velocity the signal at the output of said integrator isrepresentative of a desired descent rate to cause a craft pitch down tofly along the center line of the glide slope beam.
 11. The apparatus ofclaim 10 further including additional algebraic summing means connectedto receive the actual descent rate, displacement and desired descentrate signals to produce a resultant flight director indicator controlsignal, and means for summing the actual descent rate and desireddescent rate signals and applying them to the input of said integratorduring a second condition of said switching means corresponding to theflight director mode so that the steady state effect of the actual rateof descent signal is effectively nullified in said additional summingmeans.
 12. The apparatus of claim 11 further including means forcontinuously modifying the displacement signal in accordance with theinstantaneous altitude of the craft from a first predetermined altitudedown to a second predetermined altitude to compensate for convergence ofthe glide slope beam, and means for continuously modifying the outputsignal of said integrator in accordance with the instantaneous craftaltitude from the second predetermined altitude to touchdown such thatthe touchdown descent rate is a prescribed fraction of the instantaneousdescent rate prevailing at the second predetermined altitude.
 13. Theapparatus of claim 10 wherein the switching means is operative uponcompletion of the synchronizing mode to disconnect the output of thealgebraic summing means from the integrator input and to connect theretothe output of said beam displacement means in a third condition of saidswitching means corresponding to the autopilot mode such that the effectof the steady state actual rate of descent signal is effectivelynullified in said algebraic summing means.
 14. The apparatus of claim 13including means for continuously modifying the displacement signal inaccordance with the instantaneous altitude of the craft from a firstpredetermined altitude down to a second predetermined altitude tocompensate for convergence of the glide slope beam, and means forcontinuously modifying the output signal of said integrator inaccordance with the instantaneous craft altitude from the secondpredetermined altitude to touchdown such that the touchdown descent rateis a prescribed fraction of the instantaneous descent rate prevailing atthe second predetermined altitude.